A resonator is an electro-mechanical device that can mechanically resonate at a resonant frequency and can convert electrical signals into mechanical vibrations, and vice versa. The combination of electrical signal conversion and mechanical resonance characteristics creates a device that has useful electrical characteristics. Specifically, the resonator may be used in an electrical oscillator circuit, which provides an electrical signal at the resonant frequency. Alternatively, the resonator may be used in an electrical filter circuit that filters electrical signals based on electrical impedances associated with the mechanical resonance characteristics of the resonator.
Certain electrical characteristics may be desirable for resonators. Motional resistance is related to the effectiveness of a resonator in converting electrical signals into mechanical vibrations, and vice versa. A resonator that has high coupling coefficients in converting signals from the electrical domain to the mechanical domain and back may provide a low motional resistance, which may be useful in many applications. A resonator having a high quality factor may enable circuits having high signal integrity and high efficiency. The resonant frequency is related to an acoustic velocity of a resonator. Higher acoustic velocities produce higher resonant frequencies, which may be useful in frequency reference circuits or in filter circuits. Thus, there is a need for a resonator that has low motional resistance, a high quality factor, and high acoustic velocity.